Dogs achieve the quiet standing posture by using a multiple-loop feedback control system involving receptors, central nervous integration and skeletal muscle activity. It is assumed that the output, -position-, is compared with a volitional reference and errors are corrected through adjustments of muscle tensions and joint angles. From this point of view, the system offers an opportunity to gain insight into the manner in which various portions of the central nervous system contribute to the integration of a complex function under conditions in which the system is executing a completely normal and physiologic form of behavior. The application of systems analysis theory and techniques, furthermore, affords the opportunity to study central nervous system functions in a quantitative manner. Dogs, trained to maintain a quiet stance, are being subjected to controlled postural disturbances introduced in the form of movement of their supporting surface. The behavior of the control system is detected in terms of movement of the center of gravity, change in joint angles and change in individual leg-muscle activity. The description of the behavior of the intact system in quantitative terms constitutes the first step toward the ultimate objective. The second step will involve a quantitative evaluation of the role played by the various channels of sensory input over somesthetic, visual and vestibular pathways. Application of the available techniques for studying neuronal function will begin in the third phase of the study. BIBLIOGRAPHIC REFERENCES: Brookhart, J.M. and Talbott, R.E. 1974 The postural response of normal dogs to sinusoidal displacement. J. Physiol. (Lond.) 243: 287-307.